In the previous financial year, Labour had needed to borrow just over £30bn to balance the books, about 2% of national output.

National debt as a share of GDP was rising but at 36% was well below the 40% ceiling set by Labour and was low both by historic and international standards.

The big deterioration in the public finances happened subsequently, both as a result of the near-collapse of the banks and due to the deep economic slump that followed.

This does not provide the whole picture, however. By 2007, the UK economy had been growing steadily for more than a decade and a half.

As Gordon Brown used to boast, there had not been a single quarter of negative economic growth since the early 1990s and unemployment had fallen steadily.

In those circumstances, the government finances should have been in better shape than they were: there should have been a sizeable surplus on the current budget – the day-to-day spending of the state – and net borrowing (which includes capital spending) should have been lower.

A second problem was that Labour believed that the strength of tax receipts was permanent when in fact the Treasury coffers were being artificially boosted by an unsustainable boom in the housing market and by the party atmosphere in the City. When the speculative activity came to an end, the tax receipts dried up and blew a gigantic hole in the public finances.

The lack of any alternative sources of growth has meant that Britain's recovery from the slump has been painfully slow, and output is still 4% below its peak in early 2008.

Both the government and the opposition are now being forced to confront the reality of this, namely that there is still going to be a chunky hole in the public finances by the time of the next election.

Labour's plan for slower deficit reduction would have meant that this would have been the case anyway, but even the more aggressive stance adopted by George Osborne means that austerity will – unless there is a rapid improvement in the prospects for the economy – continue for the first two years of the next parliament.

The argument deployed by Miliband and his shadow chancellor Ed Balls has some merit. Osborne admitted in last November's autumn statement that sluggishness of growth would mean he would have to borrow well over £110bn more than he had originally planned.

Yet the opposition has so far failed to convince a sceptical public that things would be much different under its modestly less severe austerity programme.